In the production of products from rubber, it is necessary to cure or “vulcanize” the uncured rubber product under timed conditions of temperature and pressure. The accurate and automatic control of rubber-curing presses is a desired result.
In the rubber-molding art, there are a number of producers of the presses and, in general, the presses are substantially the same in terms of the physical equipment provided. However, the production of the rubber products is very individualized, not only between the companies that produce the products, but also within the product line. For example, a tire company will vary its formula for the operation of the press depending upon the intended lifetime (in terms of miles) of the tire.
It is well-known in the art to provide direct digital control of the rubber molding press. A notable point in this art is U.S. Pat. No. 4,344,142, to Diehr in 1982, which introduced the concept of providing thermocouple data from inside the mold to a computer tasked with controlling the operation of the mold. In the computer, a time-temperature relationship from physical chemistry was applied to the thermocouple data to monitor the time elapsed since the mold was closed and to re-calculate, in real time, the time remaining until a desired cure has been achieved, at which point the mold is automatically opened and the cured product removed.
In the rubber-molding art, as exemplified by U.S. Pat. No. 6,158,998 to Irie, the heat and pressure are supplied by a “heating/pressurizing medium” that is supplied to the interior of the mold in which the product is contained. Those of skill in this art will quickly recognize that the most commonly used “heating/pressurizing medium” is steam.
Improvements in the curing models implemented in the control computer and the ability to monitor mold temperature and pressure are limited, however, so long as precise control of the “heating/pressurizing medium” is not available. The current manner of managing steam flow to the mold is by pneumatic control of a valve, using compressed air.
It is therefore an unmet advantage of the prior art to provide a control of the heating/pressurizing medium for a rubber-molding press in a digital manner.